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PDF LT1121-3.3 Data sheet ( Hoja de datos )
| Número de pieza | LT1121-3.3 | |
| Descripción | Micropower Low Dropout Regulators | |
| Fabricantes | Linear | |
| Logotipo |  |
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LT1121/LT1121-3.3/LT1121-5
Micropower Low Dropout
Regulators with Shutdown
FEATURES
n 0.4V Dropout Voltage
n 150mA Output Current
n 30µA Quiescent Current
n No Protection Diodes Needed
n Adjustable Output from 3.75V to 30V
n 3.3V and 5V Fixed Output Voltages
n Controlled Quiescent Current in Dropout
n Shutdown
n 16µA Quiescent Current in Shutdown
n Stable with 0.33µF Output Capacitor
n Reverse Battery Protection
n No Reverse Current with Input Low
n Thermal Limiting
n Available in the 8-Lead SO, 8-Lead PDIP, 3-Lead
SOT-23 and 3-Lead TO-92 Packages
APPLICATIONS
n Low Current Regulator
n Regulator for Battery-Powered Systems
n Post Regulator for Switching Supplies
DESCRIPTION
The LT®1121/LT1121-3.3/LT1121-5 are micropower low
dropout regulators with shutdown. These devices are ca-
pable of supplying 150mA of output current with a dropout
voltage of 0.4V. Designed for use in battery-powered sys-
tems, the low quiescent current, 30µA operating and 16µA
in shutdown, makes them an ideal choice. The quiescent
current is well-controlled; it does not rise in dropout as it
does with many other low dropout PNP regulators.
Other features of the LT1121/LT1121-3.3/LT1121-5 include
the ability to operate with very small output capacitors.
They are stable with only 0.33µF on the output while most
older devices require between 1µF and 100µF for stability.
Small ceramic capacitors can be used, enhancing manu-
facturability. Also the input may be connected to ground
or a reverse voltage without reverse current flow from
output to input. This makes the LT1121 series ideal for
backup power situations where the output is held high and
the input is at ground or reversed. Under these conditions
only 16µA will flow from the output pin to ground.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V Battery-Powered Supply with Shutdown
8 IN
OUT 1
3.3VOUT
150mA
5V
LT1121-3.3
+ 1μF
SOLID TANTALUM
5 SHDN
GND
3
VSHDN (PIN 5) OUTPUT
<0.25
OFF
>2.8 ON
NC ON
LT1121 • TA01
Dropout Voltage
0.5
0.4
0.3
0.2
0.1
0
0 20 40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
LT1121 • TA02
1121fg
1
1 page  
LT1121/LT1121-3.3/LT1121-5
TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
0.7
0.6
TJ ≤ 125°C
0.5
0.4
TJ ≤ 25°C
0.3
0.2
0.1
0
0
= TEST POINTS
20 40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
1121 G01
LT1121-3.3
Quiescent Current
120
100
RTJLO=A2D5=°C∞
80
VSHDN = OPEN
60
40
20 VSHDN = 0V
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
1121 G04
LT1121-3.3
Output Voltage
3.38
IOUT = 1mA
3.36
3.34
3.32
3.30
3.28
3.26
3.24
3.22
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1121 G07
Dropout Voltage
0.7
0.6 ILOAD = 150mA
0.5 ILOAD = 100mA
0.4
0.3 ILOAD = 50mA
0.2 ILOAD = 1mA
0.1
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1121 G02
LT1121-5
Quiescent Current
120
100
RTJLO=A2D5=°C∞
80
VSHDN = OPEN
60
40
20 VSHDN = 0V
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
1121 G05
LT1121-5
Output Voltage
5.08
IOUT = 1mA
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1121 G08
Quiescent Current
50
VIN = 6V
RLOAD =
∞
40
VSHDN = OPEN
30
20 VSHDN = 0V
10
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1121 G03
LT1121
Quiescent Current
120
100
RTJLO=A2D5=°C∞
VOUT = VADJ
80
VSHDN = OPEN
60
40
20 VSHDN = 0V
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
1121 G06
LT1121
Adjust Pin Voltage
3.83 IOUT = 1mA
3.81
3.79
3.77
3.75
3.73
3.71
3.69
3.67
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1121 G09
1121fg
5
5 Page 
LT1121/LT1121-3.3/LT1121-5
APPLICATIONS INFORMATION
resistor is shown in Table 6. The LT1121 is a micropower
device and output transient response will be a function of
output capacitance. See the Transient Response curves
in the Typical Performance Characteristics. Larger values
of output capacitance will decrease the peak deviations
and provide improved output transient response. Bypass
capacitors, used to decouple individual components
powered by the LT1121, will increase the effective value
of the output capacitor.
Table 6. Suggested Series Resistor Values
OUTPUT CAPACITANCE
SUGGESTED SERIES RESISTOR
0.33µF
2Ω
0.47µF
1Ω
0.68µF
1Ω
>1µF None Needed
Protection Features
The LT1121 incorporates several protection features
which make it ideal for use in battery-powered circuits.
In addition to the normal protection features associated
with monolithic regulators, such as current limiting and
thermal limiting, the device is protected against reverse
input voltages, reverse output voltages, and reverse volt-
ages from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal opera-
tion, the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages of
30V. Current flow into the device will be limited to less
than 1mA (typically less than 100µA) and no negative
voltage will appear at the output. The device will protect
both itself and the load. This provides protection against
batteries that can be plugged in backwards.
For fixed voltage versions of the device, the output can
be pulled below ground without damaging the device. If
the input is open circuit or grounded the output can be
pulled below ground by 20V. The output will act like an
open circuit, no current will flow out of the pin. If the input
is powered by a voltage source, the output will source the
short-circuit current of the device and will protect itself by
thermal limiting. For the adjustable version of the device,
the output pin is internally clamped at one diode drop
below ground. Reverse current for the adjustable device
must be limited to 5mA.
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled
to ground, pulled to some intermediate voltage, or is left
open circuit. Current flow back into the output will vary
depending on the conditions. Many battery-powered cir-
cuits incorporate some form of power management. The
following information will help optimize battery life. Table
7 summarizes the following information.
The reverse output current will follow the curve in Figure
2 when the input pin is pulled to ground. This current
flows through the output pin to ground. The state of the
shutdown pin will have no effect on output current when
the input pin is pulled to ground.
In some applications it may be necessary to leave the
input to the LT1121 unconnected when the output is held
high. This can happen when the LT1121 is powered from
a rectified AC source. If the AC source is removed, then
the input of the LT1121 is effectively left floating. The
reverse output current also follows the curve in Figure 2
if the input pin is left open. The state of the shutdown pin
will have no effect on the reverse output current when the
input pin is floating.
100
90
TJ = 25°C
VIN < VOUT
80
CURRENT FLOWS
INTO OUTPUT PIN
70 TO GROUND
60 LT1121
50 (VOUT = VADJ)
40
LT1121-3.3
30
20
10 LT1121-5
0
012345 678
OUTPUT VOLTAGE (V)
9 10
1121• F02
Figure 2. Reverse Output Current
1121fg
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1121-3.3.PDF ] | |
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